[U-Boot] [PATCH] ARM: imx: fsl_esdhc: fix usage of low 4 bits of sysctl register

[Eric Nelson]

Hi Fabio and Hector,

On 12/04/2015 10:43 AM, Eric Nelson wrote:
> On 12/04/2015 10:38 AM, Eric Nelson wrote:
>> On 12/04/2015 10:32 AM, Eric Nelson wrote:
>>> The low four bits of the SYSCTL register are reserved on the USDHC
>>> controller on i.MX6 and i.MX7 processors, but are used for clocking
>>> operations on earlier models.
>>>
>>> Guard against their usage by hiding the bit mask macros on those
>>> processors.
>>>
>>> These bits are used to prevent glitches when changing clocks on
>>> i.MX35 et al. Use the RSTA bit instead for i.MX6 and i.MX7.
>>>
>>> From the i.MX6DQ RM:
>>> 	To prevent possible glitch on the card clock, clear the
>>> 	FRC_SDCLK_ON bit when changing clock divisor value(SDCLKFS
>>> 	or DVS in System Control Register) or setting RSTA bit.
>>>
>>> Signed-off-by: Eric Nelson <eric at nelint.com>
>>
>> I forgot to add an in-reply-to header.
>>
>> http://lists.denx.de/pipermail/u-boot/2015-December/thread.html#236651
>>
>>
> 
> Fabio, I haven't been able to reproduce the "mmc erase/ENGcm03648"
> issue (with or without a code change) for a couple of hours now.
> 
> Can you give this a spin?
> 
> It seems unlikely to address the issue unless what we're seeing is a
> side effect of a glitch while switching clocks.
> 
> 

I switched back to a v2014.10 release and am able to reproduce the
issue at will.

The sysctl patch had no effect, but adding an #ifndef around the
ENGcm03648 block allows things to proceed.

+#ifndef CONFIG_FSL_USDHC
        /* Workaround for ESDHC errata ENGcm03648 */
        if (!data && (cmd->resp_type & MMC_RSP_BUSY)) {
...

Since the need to poll the DAT0 line is only documented in the
errata for the i.MX35, I wonder if this isn't the right thing to do.

The CC bit of irqstat does indicate that the command completed
and without error (I'm seeing values of 1 in irqstat).

>From what I can tell, the linux kernel doesn't do this test and
doesn't appear to have any trouble.

What code base are you running against (u-boot-imx/master)?

What do you see if you do the same?

I had been testing against v2015.10 and the board I'm testing isn't
upstream, so I can't easily bisect.

Please advise,


Eric